1. Field of the Invention
The present invention relates to an improved process for the conversion of an aromatic hydrocarbon in the presence of a low valent titanium compound on an inorganic oxide catalyst.
The invention is described with reference to the alkylation of benzene with ethylene, transalkylation of ethylbenzene and methyl group containing aromatic compounds in the presence of the catalyst. The invention can also be used in alkylation and isomerization of alkylaromatic compounds.
2. Description of the Prior Art
Conversion of aromatic hydrocarbons is well known in industry. Some of the aromatic conversion reactions which occur include alkylation of aromatic hydrocarbons with an alkylating agent such as an olefin, disproportionation or transalkylation of alkyl aromatics and isomerization of alkyl aromatics such as xylenes, and of dialkyl and higher substituted aromatics.
Of special interest, has been the alkylation of benzene to ethylbenzene, or cumene. Ethylbenzene may be dehydrogenated to make styrene, while cumene is used for the production of phenol and acetone. Cumene is also dehydrogenated to form methylstyrene, in a process similar to that used to convert ethylbenzene to styrene. Ethylbenzene and cumene may also be used as blending components in aviation gasoline because of their high octane number.
It is well known that cumene can be sythesized from benzene and propylene using a catalyst of AlCl.sub.3, SPA, or BF.sub.3. SPA is a generally accepted abbreviation for solid phosphoric acid catalyst, or phosphoric acid which is adsorbed on kieselguhr or other support.
Ethylbenzene can be synthesized from benzene and ethylene using AlCl.sub.3 in the presence of catalyst activating agents or co-catalysts such as HCl or alkyl chlorides but SPA is not used commercially for this purpose. AlCl.sub.3 is a very popular alkylation catalyst, because of its high activity and good yield. Unfortunately, the catalyst operates as a slurry or sludge which is unruly to handle on a commercial scale, and also is corrosive. A current improved process employs reduced amounts of AlCl.sub.3 at higher reaction temperatures. The highly reactive nature of this Friedel-Crafts metal halide catalyst, AlCl.sub.3, is desirable when attempting to alkylate benzene with ethylene, because less active catalyst systems do not work.
Another process employs a high silica/alumina ratio zeolite catalyst utilized in a fixed bed process. Since the catalyst activity is weak compared to Friedel-Crafts metal halide catalysts and the reaction is necessarily performed in vapor phase, the reaction temperature is quite high and in the range of 650.degree.-900.degree. F. In this process, the benzene to ethylene ratio is relatively high to minimize frequent catalyst regenerations. The yield of alkylated products is less than expected from Friedel-Crafts metal halide catalyst process, even at high benzene to ethylene ratios which requires more frequent catalyst regenerations.
Another highly selective catalyst system has been developed for the alkylation of benzene with olefins. This catalyst comprises boron trifluoride. The trifluoride catalyst system is exceptionally active and permits operation with dilute olefin streams, but it requires the continuous addition of BF.sub.3 to maintain catalyst activity. High catalyst activity also leads to oligomerization of olefins so that the contact time of olefins with BF.sub.3 catalyst should be as short as possible. This catalyst is also exceptionally water sensitive, as water not only destroys the catalyst, but produces very corrosive solutions which attack downstream processing units. BF.sub.3 also frequently appears in the product, and must be removed therefrom.
Because of the interest in alkylation of benzene with ethylene and transalkylation of ethylbenzene with olefins, and because of the inadequacies of existing catalyst systems, I studied the work that others had done, and made exhaustive investigations to determine if it would be possible to find a catalyst which would have the activity and selectivity required to produce an acceptable product, while making maximum use of existing petroleum resources.
A highly active catalyst was sought, to permit operation, at attractive temperatures with less utility cost, cost of construction, and to operate with less catalyst. In new units this would mean smaller, and cheaper reactor vessels, while in existing units it would mean that an increase in capacity could be obtained by changing catalyst in an existing reactor vessel with minor modifications.
There has been extensive work done with Ti catalysts, though most work occurred in conjunction with studies of Ziegler Natta catalysts. The closest prior art known in U.S. Pat. No. 2,381,481 (Class 260-683.15), U.S. Pat. No. 2,951,885 (Class 260-671), U.S. Pat. No. 2,965,686 (Class 260-671) and U.S. Pat. No. 3,153,634 (Class 252-429).
In U.S. Pat. No. 2,381,481, preparation and use of a catalyst prepared by treating alumina gel with fluorotitanic acid is disclosed. This catalyst is used for polymerization of olefins to heavier hydrocarbons, and also for alkylation of paraffins with olefins, the latter when operating at high temperatures, between 700.degree. and 900.degree. F. or higher. No mention is made of alkylation of aromatics with olefinic hydrocarbons or transalkylation of polyalkybenzenes.
In U.S. Pat. No. 2,951,885, there is disclosed the use of titanium trihalide on activated alumina or other activated acidic oxide for alkylation of benzene with olefins. The catalyst is originally a tetrachloride, subsequently reduced to the trichloride with an alkali metal such as sodium, lithium, or potassium. The examples show that this catalyst will alkylate benzene with ethylene.
In U.S. Pat. No. 2,965,686, the thrust of the application was to develop a titanium subchloride catalyst. The subchloride catalyst was prepared by reacting titanium metal, in the form of turnings, with titanium tetrachloride. The patentee speculated, but gave no examples, showing that it would be possible to form the subchloride by reduction of titanium tetrachloride with hydrogen.
In U.S. Pat. No. 3,153,634, there is disclosed the use of titanium subhalides in a polymerization reaction. The patentee is probably describing catalyst to make solid polymer, as he discussed production of solid polymer products. The patentee seems to teach that the halides all act equivalently. The patentee in U.S. Pat. No. 3,153,634 taught the very antithesis of applicant's process, on page 3 line 65-75 where he mentions use of benzene as an inert solvent to hold dissolved olefins, rather than as a reactant.